2.2. Cultivation in bioreactor
Overall structure of bioreactor used in this work is shown in Fig. 1. DO sensor and pH electrode (Millipore) were installed in the vessel. A 3.0-L glass vessel containing 2.4 L of medium was used for starting batch culture. As shown in detail in Fig. 1B–D, a double-elliptic plate (RM) was used for reciprocal mixing (stroke = 20 mm), and conventional 6 flat turbine (6FT) and elephant ear impeller (EE) were used for rotary mixing. Cells, prepared in 100-mm dishes and 100-mL flask with shaking, were transferred into the bioreactor to start cultivation at 105 cells/mL. Bioreactors were operated at Pv (power per unit volume) 36 W/m3, which is equivalent to 135 rpm for 6FT mixing, 140 rpm for EE mixing, and 80 mm/s (= 2.0 Hz) for reciprocal mixing.